/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.lee.util.concurrent;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicReference;

import com.lee.util.Assert;

/**
 * A {@link com.lee.util.concurrent.ListenableFuture ListenableFuture} whose value can be set via {@link #set(Object)}
 * or {@link #setException(Throwable)}. It may also be cancelled.
 *
 * <p>
 * Inspired by {@code com.google.common.util.concurrent.SettableFuture}.
 *
 * @author Mattias Severson
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class SettableListenableFuture<T> implements ListenableFuture<T> {

    private final SettableTask<T> settableTask;

    private final ListenableFutureTask<T> listenableFuture;

    public SettableListenableFuture() {
        this.settableTask = new SettableTask<T>();
        this.listenableFuture = new ListenableFutureTask<T>(this.settableTask);
    }

    /**
     * Set the value of this future. This method will return {@code true} if the value was set successfully, or
     * {@code false} if the future has already been set or cancelled.
     * 
     * @param value the value that will be set.
     * @return {@code true} if the value was successfully set, else {@code false}.
     */
    public boolean set(T value) {
        boolean success = this.settableTask.setValue(value);
        if (success) {
            this.listenableFuture.run();
        }
        return success;
    }

    /**
     * Set the exception of this future. This method will return {@code true} if the exception was set successfully, or
     * {@code false} if the future has already been set or cancelled.
     * 
     * @param exception the value that will be set.
     * @return {@code true} if the exception was successfully set, else {@code false}.
     */
    public boolean setException(Throwable exception) {
        Assert.notNull(exception, "'exception' must not be null");
        boolean success = this.settableTask.setException(exception);
        if (success) {
            this.listenableFuture.run();
        }
        return success;
    }

    @Override
    public void addCallback(ListenableFutureCallback<? super T> callback) {
        this.listenableFuture.addCallback(callback);
    }

    @Override
    public void addCallback(SuccessCallback<? super T> successCallback, FailureCallback failureCallback) {
        this.listenableFuture.addCallback(successCallback, failureCallback);
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        this.settableTask.setCancelled();
        boolean cancelled = this.listenableFuture.cancel(mayInterruptIfRunning);
        if (cancelled && mayInterruptIfRunning) {
            interruptTask();
        }
        return cancelled;
    }

    @Override
    public boolean isCancelled() {
        return this.listenableFuture.isCancelled();
    }

    @Override
    public boolean isDone() {
        return this.listenableFuture.isDone();
    }

    /**
     * Retrieve the value.
     * <p>
     * Will return the value if it has been set via {@link #set(Object)}, throw an
     * {@link java.util.concurrent.ExecutionException} if it has been set via {@link #setException(Throwable)} or throw
     * a {@link java.util.concurrent.CancellationException} if it has been cancelled.
     * 
     * @return The value associated with this future.
     */
    @Override
    public T get() throws InterruptedException, ExecutionException {
        return this.listenableFuture.get();
    }

    /**
     * Retrieve the value.
     * <p>
     * Will return the value if it has been set via {@link #set(Object)}, throw an
     * {@link java.util.concurrent.ExecutionException} if it has been set via {@link #setException(Throwable)} or throw
     * a {@link java.util.concurrent.CancellationException} if it has been cancelled.
     * 
     * @param timeout the maximum time to wait.
     * @param unit the time unit of the timeout argument.
     * @return The value associated with this future.
     */
    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        return this.listenableFuture.get(timeout, unit);
    }

    /**
     * Subclasses can override this method to implement interruption of the future's computation. The method is invoked
     * automatically by a successful call to {@link #cancel(boolean) cancel(true)}.
     * <p>
     * The default implementation does nothing.
     */
    protected void interruptTask() {}

    private static class SettableTask<T> implements Callable<T> {

        private static final String NO_VALUE = SettableListenableFuture.class.getName() + ".NO_VALUE";

        private final AtomicReference<Object> value = new AtomicReference<Object>(NO_VALUE);

        private volatile boolean cancelled = false;

        public boolean setValue(T value) {
            if (this.cancelled) { return false; }
            return this.value.compareAndSet(NO_VALUE, value);
        }

        public boolean setException(Throwable exception) {
            if (this.cancelled) { return false; }
            return this.value.compareAndSet(NO_VALUE, exception);
        }

        public void setCancelled() {
            this.cancelled = true;
        }

        @SuppressWarnings("unchecked")
        @Override
        public T call() throws Exception {
            if (value.get() instanceof Exception) { throw (Exception) value.get(); }
            return (T) value.get();
        }
    }

}
